Creating tiled TIFF files with IDL code
Anonym
The code example shown at the bottom, writes a TIFF image using tiled image format instead of the normal TIFF image format. Standard TIFF images use strips that span all the way across the X dimension, and is only split in the Y dimension. According to the TIFF specification document, section 15:
For low-resolution to medium-resolution images, the standard TIFF method of breaking the image into strips is adequate. However high-resolution images can be accessed more efficiently—and compression tends to work better—if the image is broken into roughly square tiles instead of horizontally-wide but vertically narrow strips.
This is a quick test to check the data type support:
IDL> data = double(dist(800,600))
IDL> tiff6_write, 'test.tif', data & help, read_tiff('test.tif')
<Expression> DOUBLE = Array[800, 600]
IDL> tiff6_write, 'test.tif', float(data) & help, read_tiff('test.tif')
<Expression> FLOAT = Array[800, 600]
IDL> tiff6_write, 'test.tif', ulong(data) & help, read_tiff('test.tif')
<Expression> ULONG = Array[800, 600]
IDL> tiff6_write, 'test.tif', long(data) & help, read_tiff('test.tif')
<Expression> LONG = Array[800, 600]
IDL> tiff6_write, 'test.tif', uint(data) & help, read_tiff('test.tif')
<Expression> UINT = Array[800, 600]
IDL> tiff6_write, 'test.tif', fix(data) & help, read_tiff('test.tif')
<Expression> INT = Array[800, 600]
IDL> tiff6_write, 'test.tif', byte(data) & help, read_tiff('test.tif')
<Expression> BYTE = Array[800, 600]
This is the code used to produce the tiled TIFF files:
function tiff6_Ifd, tag, type, count,valueOffset
compile_opt idl2,logical_predicate
typelen = [1,1,1,2,4,8,1,1,2,4,8,4,8]
ifd = { tiff6ifd, tag: 0us, type: 0us, count: 0ul, valueOffset: 0ul }
ifd.tag = tag
ifd.type = type
ifd.count = count
len = typelen[type]*count
if len le 4 then begin
case type of
3: ifd.valueOffset= ulong([uint(valueOffset), 0us],0)
4: ifd.valueOffset= ulong(valueOffset)
8: ifd.valueOffset= ulong([fix(valueOffset), 0s],0)
9: ifd.valueOffset= ulong(long(valueOffset),0)
11: ifd.valueOffset= ulong(float(valueOffset),0)
else: if max(type eq [1,2,6,7]) then begin
ifd.valueOffset = ulong([byte(valueOffset), 0b,0b,0b],0)
endif else message, 'Unsupported type: '+strtrim(type,2)
endcase
endif else begin
ifd.valueOffset = ulong(valueOffset)
if arg_present(valueOffset) then begin
valueOffset += len
endif
endelse
return, ifd
end
pro tiff6_write, filename, data
compile_opt idl2,logical_predicate
;header
byteord = byte(1us,0) ? 'II' : 'MM'
header = { byteord: byteord, magic: 42us, ifdOffset: 8ul }
numIfd = 18us
;determine length and type
sz = size(data, /struct)
sz.dimensions >= 1
h = hash('BYTE',[1,1,1],'INT',[8,2,2],'UINT',[3,2,1],'LONG',[9,4,2], $
'ULONG',[4,4,1],'FLOAT',[11,4,3],'DOUBLE',[12,8,3])
if h.HasKey(sz.type_name)then begin
info = (orderedhash(list('type','len','frmt'), $
list(h[sz.type_name],/extract))).ToStruct()
endif else message, 'Unsupported type: '+sz.type_name
;strings need to be 0 terminated and even length
software = [byte('IDL 8.3'),0b]
datetime = [byte(string(systime(/julian), format= $
'(c(cyi4.4,":",cmoi2.2,":",cdi2.2,"",cHi2.2,":",cmi2.2,":",csi2.2))')),0b]
;compute tile info
tileSize = 128
tileByteSize = info.len*tileSize^2
n = sz.dimensions/tileSize + (sz.dimensions mod tileSize ne 0)
ntiles = n[0]*n[1]
ptr = 8 + 2 + numIfd*12 + 4
;fill in fields
ifds = list()
ifds.Add, tiff6_ifd(256, 4, 1, sz.dimensions[0]) ; width
ifds.Add, tiff6_ifd(257, 4, 1, sz.dimensions[1]) ; length
ifds.Add, tiff6_ifd(258, 3, 1, info.len*8) ; bits
ifds.Add, tiff6_ifd(259, 3, 1, 1) ; compression
ifds.Add, tiff6_ifd(262, 3, 1, 1) ; photometric interpretation
ifds.Add, tiff6_ifd(274, 3, 1, 1) ; orientation
ifds.Add, tiff6_ifd(277, 3, 1, 1) ; samples per pixel
ifds.Add, tiff6_ifd(282, 5, 1, ptr) ; xresolution
ifds.Add, tiff6_ifd(283, 5, 1, ptr) ; yresolution
ifds.Add, tiff6_ifd(284, 3, 1, 1) ; planar configuration
ifds.Add, tiff6_ifd(296, 3, 1, 2) ; resolution unit
ifds.Add, tiff6_ifd(305, 2, n_elements(software), ptr) ; software
ifds.Add, tiff6_ifd(306, 2, n_elements(datetime), ptr) ; datetime
ifds.Add, tiff6_ifd(322, 4, 1, tileSize) ; tile width
ifds.Add, tiff6_ifd(323, 4, 1, tileSize) ; tile length
ifds.Add, tiff6_ifd(324, 4, ntiles, ptr) ; tile offsets
ifds.Add, tiff6_ifd(325, 4, ntiles, ptr) ; tile byte counts
ifds.Add, tiff6_ifd(339, 3, 1, info.frmt) ; sample format
;fields that require more data
aux = list()
aux.Add, ulong([100,1])
aux.Add, ulong([100,1])
aux.Add, software
aux.Add, datetime
aux.Add, ulindgen(ntiles, start=ptr, increment=tileByteSize)
tmp = replicate(tileByteSize, ntiles)
aux.Add, tmp
if numifd ne n_elements(ifds) then message, 'IFD size mismatch'
;write to file
openw, lun, filename,/get_lun
writeu, lun, header
writeu, lun, numIfd
writeu, lun, ifds.ToArray()
writeu, lun, 0ul ; next IFD, formulti image
foreach x, aux do writeu, lun, x
tmp = make_array([tileSize,tileSize], type=size(data,/type))
for j=0, n[1]-1 do begin
ys = j*tileSize
ye = (j*tileSize + tileSize-1) < (sz.dimensions[1]-1)
for i=0, n[0]-1 do begin
xs = i*tileSize
xe = (i*tileSize +tileSize-1) < (sz.dimensions[0]-1)
tmp[0,0] = data[xs:xe,ys:ye]
writeu, lun, tmp
endfor
endfor
free_lun, lun
end